This application is based on application No. 2000-179803 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the invention
The present invention relates to a color image forming apparatus and more particularly to an image forming apparatus such as a printer, a copying machine, a facsimile machine and a multi function printer in which a toner image is formed on an intermediate transfer member and then transferred to a recording medium such as a paper or an OHP film sheet (i.e., a film sheet for an overhead projector).
2. Description of the Related Art
A so-called tandem-type color image forming apparatus is conventionally known in which a plurality of image forming units storing toners of different colors are arranged along an intermediate transfer belt, as disclosed in Japanese laid-open Patent Application No. HEI 7-28294.
With such an image forming apparatus, images of respective colors are formed, one upon another, on the intermediate transfer belt by respective image forming units, and the resulting composite color image is transferred onto a sheet. The sheet is subsequently transported through a fixing unit for thermally fixing the image on the sheet. Thereafter, the sheet is discharged to a discharged sheet tray.
In the above-described prior art image forming apparatus, the feeding of a sheet on which an image is to be transferred may be delayed, due to a slip for example, relative to the image formed on the intermediate transfer belt in the respective image forming units, so that the sheet may not be transported in time for the transferring of the image. In such a case, the operation of the apparatus is compulsorily interrupted so that the sheet, which is on the way of transportation, is removed by the user, and the toner image on the intermediate transfer belt is removed by scraping off the toners.
With such a method, however, the interruption of the operation greatly deteriorates the image forming productivity. Moreover, the toners having formed the removed toner image as well as the sheet removed on the way of transportation are wasted if they are not reused.
Further, if a sheet of thick paper or OHP film sheet is fed in spite of a printing instruction for an ordinary sheet and the image fixing is performed on the same condition as for an ordinary sheet, heat is greatly absorbed by the sheet itself. As a result, the fixing of the image becomes insufficient, so that it is impossible to obtain an image having good color development.
It is, therefore, an object of the present invention to provide an image forming apparatus which is capable of continuing the image forming operation even when the feeding of a sheet is delayed relative to an image on the intermediate transfer belt.
Another object of the present invention is to provide an image forming apparatus which is capable of sufficiently fixing an image and providing an image of good color development.
For accomplishing the above-described objects, an image forming apparatus in accordance with the present invention comprises: a rotatable intermediate transfer member; an image forming device for forming a toner image of a different color images on the intermediate transfer member; a transferring device for transferring the toner image formed on the intermediate transfer member onto a sheet; a fixing device for fixing the toner image transferred on the sheet to the sheet; and an image forming operation controller for judging whether or not a condition for transferring or fixing an image on the sheet is met and for controlling an image forming operation based on the judgment.
According to another aspect of the present invention, an image forming apparatus, comprises: a rotatable intermediate transfer belt; a plurality of image forming units each for forming an image of a different color on the intermediate transfer belt, the units being arranged along the intermediate transfer belt; a transferring device for transferring the image formed on the intermediate transfer belt onto a recording medium; and a controller for judging whether or not a condition for transferring an image on the recording medium is met and for controlling an image forming operation based on the judgement.